Alterations of the Temporomandibular Joint on Magnetic Resonance Imaging according to Growth and Development in Schoolchildren.

The paper explains the alterations of the temporomandibular joint (TMJ) visualized by magnetic resonance imaging (MRI) according to the growth and development of schoolchildren. Appearance and disappearance of a "double contour-like structure" (DCLS) of the mandibular condyle on MRI according to the growth and development of schoolchildren were demonstrated. In addition, possible constituents of DCLS and the significance of detection of DCLS on MRI were also speculated. The relationship between red marrow and yellow marrow in the articular eminence of temporal bone, the disappearance of DCLS, and alterations of the mandibular condyle have been elucidated.

Effect of 8-hour intermittent orthodontic force on osteoclasts and root resorption.

INTRODUCTION: The duration of force application is an important factor in optimizing orthodontic tooth movement with less root resorption. It has previously been shown that the amount of tooth movement achieved by 8-hour intermittent force application exceeds what would be the expected by the duration. The purpose of this study was to compare osteoclast recruitment and the extent of root resorption in response to an 8-hour intermittent force regimen with those from a continuous force. METHODS: Rat molars (n = 110) were assigned to 3 groups: 8-hour intermittent force, continuous force, and control. A coil spring that exerted 40 cN of force was suspended between the maxillary first molars and the incisors. At 1, 3, 5, 7, and 14 days, osteoclast numbers, osteoclast surfaces, and root resorption were quantified histomorphometrically in the undecalcified sections and statistically analyzed. RESULTS: At the mesial sites, osteoclast numbers in the intermittent force group were 100.5% of the continuous force group, and osteoclast surfaces in the intermittent force group were 68.2% of the continuous force group. At the mesial sites, root resorption of the intermittent group was approximately 30.0% of the continuous group (P <0.01). CONCLUSIONS: Our results show that an 8-hour intermittent force efficiently recruits osteoclasts while causing minimal root resorption.

Relationship between cortical bone formation on mandibular condyles and alternation of the magnetic resonance signals characteristic of growth.

INTRODUCTION: The purpose of this study was to elucidate the significance of double contour-like structures (DCLS) relative to the maturity of mandibular condyles and the possible constituents of DCLS. We evaluated the relationship between the alternation of DCLS and the ossification on the top of mandibular condyles. METHODS: In 36 subjects, aged 9 to14 years at the first examination, magnetic resonance imaging characteristics of the mandibular condyles were obtained from fast spin echo intermediate-weighted images and T2-weighted images; 2 or 3 years later, magnetic resonance images were again obtained from 23 of the same 36 subjects. RESULTS: A significant relationship was found between the absence of DCLS and the continuity of void-signal lines on the tops of the mandibular condyles. DCLS disappeared, and the void-signal lines on the tops of the mandibular condyles became continuous as the children grew. The top of DCLS was seen as a hypersignal on T2-weighted images. CONCLUSIONS: Alternations of DCLS might be a useful criterion for evaluating the maturity of mandibular condyles in children. Possible constituents of DCLS might be hypervascular loose fibrous tissue and a proliferation of cartilage accompanied by active ossification on the tops of the mandibular condyles.

Expansion of the mandibular arch in children during the mixed dentition period--a clinical study.

A review of the dental literature revealed relatively few studies on the expansion of the mandibular dental arch. The present study attempted expansion of the mandibular arch using a Bihelix appliance. The subjects were 16 children, exhibiting crowding, age ranges from 7 to 11 years. The mandible was expanded 2.0 mm every 3 months. Significant expansion, not only of the individual tooth inter-arch dimensions but also of the overall arch length, was obtained during the period of incisor tooth replacement. The mode of expansion was classified as follows: Type I, those, which showed no effect on the apical base; Type II, those which showed no consistency of the measurement lines. In this study, 6 of 16 cases were classified as type I and 10 cases as type II. Expansion was continued over a period of 1.5 to 3 years. We concluded that considerable lateral expansion of the mandibular arch is possible using the Bihelix appliance. It is suggested that this might contribute greatly to non-extraction orthodontic treatment. Further studies are recommended.

Correlation between the appearance of neuropeptides in the rat trigeminal ganglion and reinnervation of the healing root socket after tooth extraction.

The neuropeptide substance P (SP) modulates bone metabolism. This study examined the temporal appearance of the neuropeptides SP and brain-derived nerve growth factor (BDNF) and their receptors (neurokinin-1 receptor (NK1-R) and Trk B, respectively) in the rat trigeminal ganglion to investigate the role of neuropeptides in healing after tooth extraction. Rats were anesthetized and their upper right first molars were extracted; the rats were sacrificed 3 hours and 1-21 days after extraction. Their trigeminal ganglion and maxilla were removed, and cryosections were prepared and immunostained using specific antibodies against SP, BDNF, NK1-R, and Trk B. In the tooth sockets after extraction, new bone and a few SP--immunoreactive nerve fibers were first seen at day 7, and bone completely filled the sockets at day 21. In the trigeminal ganglion, the proportions of NK1-R-, BDNF-, and Trk B-immuno-reactive neurons changed similarly, i.e., they initially decreased, increased rapidly to -maximum levels by day 3, and then decreased gradually to control levels until 21 days. These findings suggest that the appearance of neuropeptides in the trigeminal ganglion, the reinnervation of SP-immunoreactive nerve fibers, and bone repair in the tooth socket during healing after extraction were correlated.

Alternation of the magnetic resonance signals characteristic of mandibular condyles during growth.

OBJECTIVE: In a previous study, we named the magnetic resonance imaging (MRI) signal that is characteristic of mandibular condyles in growing children the "double contour-like structure" (DCLS). In the current study, we evaluated the alternating appearance and disappearance of the DCLS in children as they grow to elucidate the significance of the DCLS. STUDY DESIGN: In 11 subjects who were 9-14 years old at the time of the first examination, MRI characteristics of mandibular condyles were sought from fast spin-echo intermediate-weighted images; 2 or 3 years later, repeat MRI were obtained from the same subjects. RESULTS: At the second examination, 10 of the 16 DCLSs detected at the first examination had disappeared. A significant relationship was found between the alternation of the DCLS and the bone marrow conversion from red to yellow in mandibular condyles. Alternation of the DCLS tended to coincide with eruption of the permanent maxillary second molars. The DCLS was also shown to appear as a hypersignal on T2-weighted images. CONCLUSIONS: Double contour-like structure signals in mandibular condyles appeared and disappeared as children grew, and these signal alternations may be useful as a criterion for the staging of mandibular condyle development in children. Possible constituents of the DCLS may be hypervascular loose fibrous tissue and a proliferation of cartilage.

Intermittent 8-hour activation in orthodontic molar movement.

The duration of force application is an important factor, together with the magnitude of force, in stimulating osteoclast recruitment in the periodontal ligament. The purpose of this study was to examine the effect of duration of intermittent versus continuous force application on the amount of molar movement in rats. Seventy-six molars of 38 rats were randomly assigned to continuous, intermittent, and sham-operation groups. A calibrated nickel-titanium coil spring exerting 40 g of initial force was suspended between the maxillary first molars and the incisors for 13 days. In the intermittent group, the coil spring was suspended for 8 hours per day. Tooth movement was measured on radiographs. There was no significant difference in the initial tooth displacement between the continuous-force and intermittent-force groups. Tooth movement at day 7 was significantly (P <.05) less in the intermittent group than in the continuous group. Actual mesial tooth movement and total tooth movement in the intermittent group were 65.9% and 73.7%, respectively, of those in the continuous group. Our results suggest that the amount of tooth movement in response to intermittent force is less than that in response to continuous force, but that the amount of tooth movement achieved by intermittent force exceeds the expected value predicted by the duration (33.3%) of force application.

Detection and significance of the characteristic magnetic resonance signals of mandibular condyles in children.

OBJECTIVE: We sought to determine the magnetic resonance imaging (MRI) characteristics of mandibular condyles in still-growing children. In addition, we also evaluated the significance of the double-contour-like structure and the conversion from red to yellow marrow characteristic of this age. METHODS: The MRI characteristics of mandibular condyles were determined by means of fast spin-echo intermediate-weighted images in subjects 9 to 14 years old. In 1 subject who developed temporomandibular joint-related clinical symptoms 1 year later, MRI was re-performed at that time. RESULTS: With the use of MRI, a total of 17 double-contour-like structures were detected in 42 temporomandibular joints of 9- to 14-year-olds, but neither 50 healthy joints of youths nor adults. In terms of bone marrow signal changes, the turning point was found to be 11 years old. In 1 subject, the double-contour-like structures were not visible on the MR images obtained 1 year after the first examination. CONCLUSION: The double-contour-like structure and the periods of conversion from red to yellow marrow may be able to be used as part of the criteria for the staging of mandibular condyle development in children.

Diagnostic image analyses of activator treated temporomandibular joint in growth and maturing stages.

This study evaluates the condylar response to activator in growth and in maturing patients using radiographs and magnetic resonance images (MRI). Seven patients (four in growth and three in maturing stages) treated for mandibular distal occlusion were studied. In all seven patients, lateral roentgen cephalograms, panoramic radiograms, and MRIs were made before and following functional treatment. All patients' mandibles advanced during treatment. Downward and forward mandibular growth was observed by superimposition of lateral cephalograms. On the condylar posterosuperior regions for both groups, double contours were sometimes observed on the panoramic radiograms following therapy. These double contours coincided with an area of high intensity in the MRIs for both groups. In the mature adult group, the double contours were more clearly observed when compared with those in the growth group. There were differences in the condylar adaptation types between the growth and mature development stages. Condylar adaptation to the newly created mandibular position was nevertheless found even in adult patients.